Introduction to Single-Group Condensation RTV Silicone Rubber

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As a subcategory of RTV silicone rubbers, single-group condensation RTV silicone rubber is made by the following procedure:

To use organic hydroxyl terminated polysiloxane which has low molecular quantity as the base rubber and it is to mix it with reinforcing agent and to dry the mixture. After it, to add crosslinking, catalyst and other additives and then to mix them together averagely in the mixer which is isolating humidity. At this time, mixed rubber is already the polymer which has multiple functional groups and to squeeze out when using it to let the functional groups in the rubbers to form unstable hydroxyl with the water in air to lead to the final condensation to crosslink the final elastomer.

It is according to categories of materials made from the crosslinking reactions between crosslinking agents and hydroxyl terminated polydimethylsiloxane, the condensation single-group RTV silicone rubbers could be divided into 7 types. It could keep elasticity in a wide temperature range between -60 and 300℃. It has good adhesion to many base materials and it has excellent cold and heating resistance. It is widely applied as adhesive, sealing agents, protection coatings and moulding materials.

If we categorize it based on the moulding quantity, it could be divided into three types: low moulding quantity, medium moulding quantity, high moulding quantity. If we categorize it by the usage, it could be divided to general type and special type. The special type usually refers to the ones which have properties like oil resistance, high adhesion, high strength, fast solidification and pollution resistance.

RTV silicone rubber could be made to rubbers which have different viscosities; the general types are fluid type, medium viscosity type and viscous type. Fluid type rubber has flowing ability, thus it is suitable to spray and pour; if there is a requirement of lower viscosity, we could penetrate some low polymers or to use dimethyl silicone oil to dilute it. Medium viscosity level rubber could just flow sufficiently and not to drop, by using it, we could get products with plain surface. It is good for coating and dipping. Viscous level rubber has viscosity of putty level therefore it could be operated manually, knives or strike-off boards, or to use calender method to paint and coat it on different types of textiles.

Single-group RTV silicone rubbers has excellent adhesions to many materials like metals, glasses, ceramics and plastics. Thus it is very convenient to use and no need to weight, blend and antifoam thus it is specifically useful for sealing and filleting. Its speed of vulcanization is determined by the vulcanizing system, the relative humidity of environment and the thickness of rubber layers. Thus to increase temperature or humidity could speed up vulcanization. The rubber could have solidification in one day. The depth and strength of solidification will be strengthening in around 3 weeks; the properties of RTV silicone rubbers could reach the best status. It is due to its vulcanization depends on water in the air, thus the speed is also affected by the dispersion speed of water in rubber layers which will limit the thickness of vulcanized rubbers thus it could only be used in the occasion that the thickness is less than 6mm. The deep side of thick products is hard to be vulcanized because the vulcanization begins with the surface and gradually enters the inside. The thicker the rubber is, the slower the speed of vulcanization is. When the deep part is facing fast solidification, we could add some rubbers and then add another one after vulcanization to reduce total vulcanization speed.

Manufacturing Procedure of Single-Group Condensation RTV Silicone Rubber

During the manufacturing process of single-group condensation RTV silicone rubber, it is a must to control the water percentages of each component. Single-group RTV silicone rubber’s manufacturing usually needs to mix base rubber, filler, paints and other additives together in rubber mixing machine and to dry under 160℃. Then to cool it down to 60℃ in the environment which isolate the humidity in air completely and bring it to the crosslinking system and mix it averagely for 20 minutes. These procedures lead to the mixture will be shaped into the form of thin layer to pass through the vacuum chamber to release the airs. Then the product will be sealed into a bottle to be stored. When we use it, we just need to take it out and let it get contact with water in air under room temperature then it will have solidification. The package of single-group RTV silicone rubbers generally use metal hoses, plastic sealed drums and metal sealed drums.

The production process could be made by different device groups according to the conditions of firms and the size of productivity of different product types. At present, the main devices used in industrial manufacturing could be kneader, high speed mixer, planetary compulsory mixer, static mixer and other common machines.

Base rubber and crosslinking agent are the main components of single-group RTV silicone rubber. The ratio of crosslinking agent and hydroxyl terminated polysiloxane is very important that it will influence the degree of crosslinking and properties of rubbers. Generally speaking, the system has many rest active functional groups which have good adhesions to many base materials. Single-group RTV silicone rubbers are regarded as adhesion glues or sealing adhesive. Besides these, it could also be considered as paints, heating resistance additives, plasticizers, dehydrating agent or antiseptics.

Summary

It is true that RTV silicone rubber is widely used and its subcategories have also been applied in many different industries and thus produced by more and more manufacturers in all over the world and the global market of RTV silicone rubber is also increasing. The simple manufacturing process and convenience of use also bring RTV silicone rubbers the popularity on the market.

All in all, as one subcategory of silicone rubber, RTV has shown very useful and effective properties to the industrial practices.